1. Field of the Invention
The present invention generally relates to systems using transponders, that is, transceivers (generally mobile) capable of communicating in a contactless and wireless fashion with a terminal.
The present invention more specifically relates to systems using transponders for the detection of a distance variation with respect to an axis of a point of an object rotating around this axis (the length variation of a radius in the case of a circular object). The present invention will be more specifically described in the context of the detection of a pressure fault in a tire.
2. Discussion of the Related Art
More and more tires are equipped with pressure sensors to detect a mis-inflation and notify the driver, a maintenance service, etc.
The emergence of transponder systems has enabled avoiding wire connections between the rim of the tire and the vehicle. The pressure sensor is then associated with a transponder capable of transmitting the information to a terminal supported by the vehicle (for example, the axle, the inside of the fender, etc.). The transponder generally is an active transponder, that is, associated with a battery (often rechargeable) providing the power required for its operation thereto. The sensor-transponder element may be supported by the rim or by the actual tire.
Other sensor types may be associated with a transponder in a tire. For example, these may be wear sensors.
The element associated with the tire comprises a sensor of the specific detected quantity (pressure, thickness of the tire, temperature), a circuit of conversion into electric signals, and a transponder for transmitting the information to the terminal. Further, to detect several quantities of different nature (for example, the pressure and the wearing), two sensors, or even two complete elements are necessary.
Due to the significant generated cost, pressure sensors are most often supported by the rims which have a longer durability. For automobile vehicles, this results in that, in case of a temporary rim change (for example, for the spare wheel or for snow tires assembled on other rims), the pressure detection function can no longer be ensured.